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News from Mars: Evidence of Falling Snow

Ever since astronomers first looked up at Mars, they discerned features that few could accurately identify. For many years, speculations about irrigation, canals, and a Martian civilization abounded, firing people’s imaginations and fiction. It was not until more recently, with the deployment of the Viking probe, that Mars’ surface features have come to be seen for what they are.

Thanks several more probes, and the tireless work of rover such as Opptorunity and Curiosity, scientists have been able to amass evidence and get a first hand look at the surface. Nevertheless, they are still hard-pressed to explain everything that they’ve seen. And while much evidence exists that rivers and lakes once dotted the landscape, other geological features exist which don’t fit that model.

However, a recent report from Brown University has presented evidence that snowfall may be one answer. It has long been known that ice exists at the polar caps, but actual snowfall is a very specific meteorological feature, one that has serious implications for early Martian conditions. This is just another indication that Mars hosted an environment that was very much like Earths.

And this is not the first time that snow on Mars has been suggested. In 2008, NASA announced having detected snow falling from Martian clouds, but it was entirely vaporized before reaching the ground. The Brown researchers claim that snowfall in the past, and buildup on the surface leading to melting and runoff, could have created many of the tributary networks observed near tall mountain-ranges.

To back this claim up, the team used a computer simulation from the Laboratoire de Météorologie Dynamique called the Mars global circulation model (GCM). This model compiles evidence about the early composition of the red planet’s atmosphere to predict global circulation patterns. And since other models predict that Mars was quite cold, the program indicated the highest probability of snowfall over the densest valley systems.

Lead researcher Kat Scanlon also relied on her background in orographic studies (science for “studying mountains”) in Hawaii to arrive at this hypothesis. This includes how tall mountains lead to divergent weather patterns on either side, with warm, wet conditions one and cold, dry ones on the other. NASA’s Curiosity rover also was intrinsic, thanks to recent information that might explain why Mars no longer displays this kind of behavior.

In short, Curiosity determined that the planet is losing its atmosphere. It has taken detailed assays of the current atmosphere, which is almost entirely carbon dioxide and about 0.6% the pressure of Earth’s at sea-level. More notably, it has used its ability to laser-blast solid samples and analyze the resulting vapor to determine that Mars has an unusually high ratio of heavy to light isotopes — most importantly of deuterium to hydrogen.

The main explanation for this is atmospheric loss, since light isotopes will escape slightly more quickly than heavy. Over billions of years, this can lead to non-standard isotope levels the show a loss of atmosphere. One major theory that might explain this loss say that about 4.2 million years ago Mars collided with an object about the size of Pluto. An impact from this body would have caused a huge expulsion of atmosphere, followed by a slow, continued loss from then on.

All of this plays into the larger question of life on Mars. Is there, or was there, ever life? Most likely, there was, as all the elements – water, atmosphere, clay minerals – appear to have been there at one time. And while scientists might still stumble upon a Lake Vostok-like reserve of microbial life under the surface, it seems most likely that Mars most fertile days is behind it.

However, that doesn’t mean that it can’t once again host life-sustaining conditions. And with some tweaking, of the ecological engineering – aka. terraforming – variety, it could once again.